Key telephone systems occupy a market between one line telephone instruments and private branch exchanges. Typically, a key telephone system utilizes a small number of telephone instruments connected to a small control unit which in turn is connected through a small number of outside lines to a central office. Each instrument has a rotary dial or push button key pad together with a plurality of push buttons each of which is associated with a corresponding one of the outside lines and contains a lamp which is lit when the corresponding line is busy and is dark when the corresponding line is free. A user can be connected to a free outside line by depressing any button having a dark lamp and can then place a call by "dialing" the desired number. Other variations of this system can utilize additional lamp carrying buttons for establishing a connection between different telephone instruments connected to the same key telephone system.
Wireless telephone devices have recently come into use. These devices comprise a stationary base unit connected to a single outside line and a separable cooperating handset unit with a rotary dial or key pad. These units are provided with cooperating transmitters and receivers whereby a user can move to the handset unit from place to place while the base unit remains stationary and yet the user can receive and originate calls using the handset unit in the same manner as if the handset unit were connected by wire conductor to the base unit in conventional manner.
This invention is directed toward an arrangement wherein a wireless telephone device can be connected to a key system via a communications interface in such manner that a user of the wireless device can use the handset unit to perform all the functions now performed by a stationary key telephone instrument and yet retain the freedom of motion that a wireless telephone device provides.